Catadioptric projection objective

ABSTRACT

Catadioptric projection objective ( 1 ) for microlithography for imaging an object field ( 3 ) in an object plane ( 5 ) onto an image field ( 7 ) in an image plane ( 9 ). The objective includes a first partial objective ( 11 ) imaging the object field onto a first real intermediate image ( 13 ), a second partial objective ( 15 ) imaging the first intermediate image onto a second real intermediate image ( 17 ), and a third partial objective ( 19 ) imaging the second intermediate image onto the image field. The second partial objective is a catadioptric objective having exactly one concave mirror and having at least one lens (L 21 , L 22 ). A first folding mirror ( 23 ) deflects the radiation from the object plane toward the concave mirror and a second folding mirror ( 25 ) deflects the radiation from the concave mirror toward the image plane. At least one surface of a lens (L 21 , L 22 ) of the second partial objective has an antireflection coating having a reflectivity of less than 0.1% for an operating wavelength of between 150 nm and 250 nm and for an angle-of-incidence range of between 0° and 30°. As an alternative or in addition, all the surfaces of the lenses of the second partial objective are configured such that the deviation from the marginal ray concentricity is greater than or equal to 20°.

This application is a Continuation application based on U.S. applicationSer. No. 12/562,693 with a filing date of Sep. 18, 2009, which claimspriority to German Patent Application No. 10 2009 037 077.3, filed onAug. 13, 2009, the respective entire disclosures of which areincorporated into the present application by reference.

FIELD OF AND BACKGROUND OF THE INVENTION

The invention relates to a catadioptric projection objective for imagingan object field in an object plane onto an image field in an image planeincluding three partial objectives, to a projection exposure apparatusfor microlithography including such a projection objective and also to amethod for producing semiconductor components and other finelystructured components using such a projection exposure apparatus.

The object field is imaged onto a first real intermediate image by thefirst partial objective of the catadioptric projection objective, thefirst intermediate image is imaged onto a second real intermediate imageby the second partial objective, and the second intermediate image isfinally imaged onto the image field in the image plane by the thirdpartial objective. In this case, the second partial objective is acatadioptric objective having exactly one concave mirror. Moreover, thecatadioptric projection objective has two folding mirrors, wherein thefirst folding mirror deflects the projection light from the object planetoward the concave mirror of the second partial objective and the secondfolding mirror deflects the projection light from the concave mirror ofthe second partial objective toward the image plane. The folding mirrorscan be embodied, e.g., either as separate elements or as two sidesurfaces of a unitary body, such as a prism covered with an appropriatereflection coating or coatings.

Catadioptric projection objectives of this type are known for examplefrom US 2009/0034061 and from US 2009/0092925.

OBJECTS AND SUMMARY OF THE INVENTION

At the lens surfaces of the lenses of the catadioptric projectionobjective, a specific proportion of the light is reflected on account ofthe difference in refractive index between air, or the gas filling, andthe lens material. Although this reflection can be reduced byantireflection coatings, it cannot be completely prevented. If theprojection light reflected at lens surfaces passes into the image plane,this so-called stray light leads to a background illumination thatreduces the contrast of the actual image.

It is an object of the invention, then, to reduce the stray light insuch projection objectives.

This involves investigating the light paths on which light can pass intothe image plane in this class of projection objectives. A light path isunderstood to mean the sequence of optical surfaces which the lightpasses through on the way from the object plane to the image plane. Inthis case, a distinction is made between the projection light path,along which the projection light is intended to pass through the opticalsurfaces of lenses or mirrors in accordance with the optical design ofthe catadioptric projection objective, and one or more stray lightpaths, along which the stray light passes into the image plane. In thecase of a stray light path, the stray light is reflected instead oftransmitted at at least one lens surface and thus leaves the projectionlight path. For determining the stray light paths, each lens surface isregarded both as a transmissive surface and as a reflective surface,wherein the reflectance of the lens surface governs the probability withwhich a light beam is transmitted or reflected. From an alternativestandpoint, the light beam can be split into a transmitted and areflected light beam, the reflectance determining the intensities of thetwo beams. Depending on how often the stray light is reflected at lenssurfaces within the projection objective, a distinction is made betweensingle reflections, double reflections, or even higher-orderreflections. Since the intensity of the reflections is dependent on theproduct of the reflectivities, single reflections with just onereflection lead to a comparatively high stray light intensity.Therefore, each single reflection has to be investigated with regard towhether it can be afforded tolerance or whether corresponding measuresfor reducing the stray light intensity on account of the singlereflection are necessary.

By virtue of the second partial objective having exactly one concavemirror and by virtue of the fact that the projection light is deflectedtoward this concave mirror by the first folding mirror and, afterreflection at the concave mirror, is deflected toward the image plane bythe second folding mirror, the lenses of the second partial objectivebetween the folding mirrors and the concave mirror are passed throughtwice. The projection light therefore passes through such a lens that ispassed through twice a first time on the way to the concave mirror and asecond time after reflection at the concave mirror. The lens surfaces ofsuch lenses that are passed through twice can bring about singlereflections by virtue of the projection light being reflected instead oftransmitted at one of the lens surfaces. In this case, a stray lightpath can form by virtue of optical surfaces being skipped which theprojection light would otherwise pass through on the way toward theconcave mirror and back again. Under certain circumstances, the straylight path can reach as far as the image plane. The stray light thenpasses through all those optical surfaces which the projection lightwould also pass through after reflection at the concave mirror startingfrom the reflective lens surface. The lenses of the second partialobjective which are passed through twice are therefore particularlyprone to generating stray light in the image plane on account of singlereflections.

In one aspect of the invention, at least one surface of a lens of thesecond partial objective is provided with an antireflection coatinghaving a reflectivity of less than 0.2% for an operating wavelength ofbetween 150 nm and 250 nm and for an angle-of-incidence range of between0° and 30°. An antireflection coating is understood to mean a coatingwhich is designed such that the reflection loss on account of the suddenchange in refractive index when the light enters the lens is reducedrelative to the reflection loss that arises if this coating is notprovided. In this case, the antireflection coatings provided here arespecified firstly by an operating wavelength and secondly by anangle-of-incidence range. The operating wavelength is understood to meanthe wavelength of the projection light at which the projection objectiveis operated. This is typically a wavelength in the DUV or VUV wavelengthrange between 150 nm and 250 nm, that is to say for example 248 nm, 193nm or 157 nm. An angle of incidence is understood to mean the angle of aray of light with respect to the surface normal at the point where theray of light impinges on the lens surface. In general, many rays impingeon a point of the lens surface with different angles of incidence, suchthat an antireflection coating has to be optimized not only for oneangle of incidence, but for an entire angle-of-incidence range. In thiscase, it is not possible to produce an antireflection coating whichcompletely prevents reflection at the lens surface; such reflection canonly be reduced. In this case, the degree of complexity of theantireflection coating increases with the degree of reduction of theresidual reflection for a predetermined angle-of-incidence range. Ingeneral, it suffices to design antireflection coatings for reducing thestray light effects as a result of double or multiple reflections sincedouble and multiple reflections predominate in projection objectiveswithout lenses that are passed through twice. A reflectivity of theantireflection coating within the angle-of-incidence range of forexample greater than 0.2% is sufficient for reducing double and multiplereflections in a manner that can be afforded tolerance. Furtherreduction of the reflectivity would make the antireflection coatingunnecessarily complex. If, by contrast, a stray light path which endswithin the image field already arises for a single reflection, then areflectivity of the antireflection coating within the angle-of-incidencerange of greater than 0.2% can lead to stray light that cannot beafforded tolerance. Precisely this risk is manifested, however, in thecase of the lenses of the second partial objective which are passedthrough twice. At least one lens surface of the lenses of the secondpartial objective is therefore covered with an antireflection coatinghaving a reflectivity of less than 0.2% for the angle-of-incidence rangeof 0° to 30° that is relevant to these lenses.

In a further aspect of the invention, the antireflection coating has areflectivity of less than 0.1% for a wavelength of between 150 nm and250 nm and for an angle-of-incidence range of between 0° and 30°.

Since, for rays having small angles of incidence in the range of 0° to20°, that is to say rays near to the optical axis, the probability ofnevertheless passing into the image plane after reflection at a lenssurface and contributing to the background illumination is particularlyhigh, in a further aspect of the invention, the lens surfaces of thelenses of the second partial objective which are passed through twiceare covered with antireflection coatings having a reflectivity of lessthan 0.1% for an angle-of-incidence range of 0° to 20° and for awavelength of between 150 nm and 250 nm.

In one embodiment of the invention, the antireflection coating has areflectivity of less than 0.05% for a wavelength of between 150 nm and250 nm and for an angle-of-incidence range of between 0° and 20°.

In a further embodiment of the invention, the antireflection coating hasa reflectivity of less than 0.02% for a wavelength of between 150 nm and250 nm and for an angle-of-incidence range of between 0° and 10°.

In a further embodiment of the invention, the antireflection coating hasa reflectivity of less than 0.2% for a wavelength of between 150 nm and250 nm and for an angle-of-incidence range of between 0° and 30° andsimultaneously a reflectivity of less than 0.1% for anangle-of-incidence range of between 0° and 20°.

In a further embodiment of the invention, the antireflection coating hasa reflectivity of less than 0.2% for a wavelength of between 150 nm and250 nm and for an angle-of-incidence range of between 0° and 30°, areflectivity of less than 0.1% for an angle of incidence range ofbetween 0° and 20° and simultaneously a reflectivity of less than 0.02%for an angle-of-incidence range of between 0° and 10°.

The complexity of an antireflection coating is manifested, inter alia,in the number of employed layers from which the antireflection coatingis constructed. In one embodiment of the invention, the antireflectioncoating includes six layers composed alternately of material having ahigh refractive index and material having a low refractive index. Inthis case, a material is designated as having a high refractive indexwhen it has, for the operating wavelength, a higher refractive indexthan the refractive index of the material having a low refractive index.

In a further embodiment of the invention, the antireflection coating hasseven layers composed alternately of material having a high refractiveindex and material having a low refractive index.

Owing to the use of at least six layers composed alternately of materialhaving a high refractive index and material having a low refractiveindex, it is possible to ensure a reflectivity of less than 0.2% overthe angle-of-incidence range of 0° to 30°.

In one embodiment of the invention, the employed material having a lowrefractive index is a dielectric material selected from the groupconsisting of magnesium fluoride, aluminum fluoride, sodium fluoride,lithium fluoride, calcium fluoride, barium fluoride, strontium fluoride,cryolite, chiolite, and combinations thereof.

In one embodiment of the invention, the employed material having a highrefractive index is a dielectric material selected from the groupconsisting of neodymium fluoride, lanthanum fluoride, gadoliniumfluoride, dysprosium fluoride, aluminum oxide, lead fluoride, yttriumfluoride, and combinations thereof.

For the arising of single reflections on account of the reflection atsurfaces of the second partial objective, consideration should be givenparticularly to those surfaces which have a deviation of the marginalray concentricity of less than 20°. Marginal ray concentricity isunderstood to mean the state in which a marginal ray is reflected backon itself on a lens surface. That is to say that the marginal ray has anangle of incidence of 0° at the lens surface. In this case, the marginalray employed is a fictitious ray which emerges in the object plane fromthe optical axis and just passes through the aperture stop of theprojection objective, that is to say has in the image plane an angle ofincidence corresponding to the maximum numerical aperture. It is afictitious marginal ray because this class of projection objectives hasan off-axis object field, that is to say that the optical axis of theprojection objective does not intersect the object plane within theobject field. This fictitious marginal ray can nevertheless be tracedmathematically since, for the ray tracing, the physical boundary ofmirrors or lenses or the vignetting by other optical elements isunimportant, rather the marginal ray is traced along the projectionlight path. What, then, is the relationship between the marginal rayconcentricity of a lens surface and the production of a singlereflection? In the case of ideal imaging, the marginal ray emerging fromthe object plane intersects the optical axis in the following imageplanes, that is to say, in the case of this class of projectionobjectives, in the plane of the first intermediate image, in the planeof the second intermediate image and in the image plane. If marginal rayconcentricity then exists for a lens surface in the second partialobjective, the marginal ray is reflected back on itself and thusintersects the optical axis again at the same location from which themarginal ray emerged. A so-called stray light intermediate image planethus arises, which coincides with the first intermediate image plane.Since the first intermediate image is an off-axis intermediate image,the first intermediate image and the stray light intermediate image aresituated on opposite sides of the optical axis. The stray lightintermediate image is thus located within the projection light path fromthe concave mirror to the image plane, such that it is possible for thestray light to pass into the image plane in a manner following theprojection light path. If the second partial objective is a 1:1objective, moreover, then the first and second intermediate image planesand thus also the stray light intermediate image plane coincide. Thestray light intermediate image is consequently generated at the locationof the second intermediate image and ultimately imaged into the imageplane by the third partial objective like the second intermediate image.A continuous stray light path right into the image plane arises onaccount of a single reflection. Lens surfaces for which marginal rayconcentricity exists or for which the deviation from the marginal rayconcentricity is less than 20° are therefore particularly critical forthe production of single reflexes and should therefore be provided withthe improved antireflection coating.

In addition to the improved antireflection coating of surfaces which aresusceptible to single reflections, the reduction of the singlereflections can already be taken into account when devising the opticaldesign of the projection objective. Thus, in a further aspect of theinvention, all the surfaces of the lenses of the second partialobjective are configured such that their deviation from the marginal rayconcentricity is greater than or equal to 20°. As a result, the straylight intermediate image is not generated at the location of the secondintermediate image and consequently, unlike the second intermediateimage itself, is not imaged into the image plane by the third partialobjective. Stray light and projection light have different beam extentsparticularly in the region of the second folding mirror. Since theextent of the second folding mirror is adapted to the extent of theprojection light beam, the stray light beam is vignetted by the physicalboundary of the second folding mirror and, as a result, does not reachthe image plane, or reaches the image plane only with a greatly reducedintensity.

For correction of the image field curvature and for chromaticcorrection, the second partial objective can have a plurality of lenses.These lenses which are passed through twice can have surfaces which leadto single reflections. In one embodiment of the invention, the secondpartial objective has exactly one lens. This reduces the number ofsurfaces to two surfaces at which single reflections can arise.

In order, however, that the imaging quality of the projection objectiveis not impaired owing to the reduction of the number of lenses in thesecond partial objective, in one embodiment of the invention, this lensis embodied as a bi-aspherical lens. In other words, this lens has anaspherical surface formed both on the front surface and on the backsurface. Further degrees of freedom are thereby obtained for ensuringthe required imaging quality.

As such, the background illumination in the image plane owing to straylight can be significantly reduced overall through: (i) the targetedconfiguration of the lens surfaces of the lenses of the second partialobjective for avoiding single reflections, (ii) covering lens surfacesthat are critical for single reflections with improved antireflectioncoatings, or (iii) a combined application of these two measures. Inorder to quantify the influence of the lens surfaces of the secondpartial objective on the stray light and the reduction thereof by themeasures proposed, the stray light is measured for example by arranginga non-luminous object within the homogeneously illuminated object fieldand imaging the object into the image plane. In this case, the object issquare, for example, and can have different edge lengths. The object isfor example a small box that absorbs the projection light. Without straylight, the object would be sharply imaged into the image plane, suchthat the intensity within the image of the object is 0% of the maximumvalue of the ambient illumination. With stray light, however, the imageof the object is not dark. The stray light intensity distribution can bedetermined from the intensity in the center of the image of the object,taking account of the dimensions of the object.

The intensity of the stray light in the center of the image of theobject varies depending on the illumination of the object and the originof the stray light. The illumination of the object can be characterizedby the pupil filling factor σ, inter alia. In the case of a pupilfilling factor of σ=0.2, the entrance pupil of the projection objectiveis illuminated only to a radius of 20% of the maximum pupil radius.Consequently, the object is only illuminated by rays which haverelatively small angles with respect to the optical axis. In the case ofa pupil filling factor of σ=1.0, by contrast, the entrance pupil of theprojection objective is fully illuminated, such that the object isilluminated by rays which assume the maximum possible values in theobject plane. If the object is illuminated with a small pupil fillingfactor, then the contribution of the stray light on account of singlereflections is greater than in the case of illumination with a largepupil filling factor, since, for rays, having large angles with respectto the optical axis, there is a greater probability of not passing rightinto the image plane after reflection at a lens surface, but rather ofbeing vignetted, for example at a lens mount. The stray lightmeasurement is therefore carried out for example for a pupil fillingfactor of σ=0.2. If the illumination system of the projection exposureapparatus does not provide this filling factor, then a pupil fillingfactor of between σ=0.2 and σ=0.3 is used for the stray lightmeasurement.

In addition to the single reflections caused by the lens surfaces of thesecond partial objective there are also further causes of stray lightwithin the image field in the image plane. Double reflections, onaccount of the double reflection at lens surfaces, have a negligibleintensity in comparison with single reflections. The stray light owingto surface or volume scattering can be distinguished from stray light onaccount of single reflections by choosing the edge length of the objectto be large enough, for example 1.0 mm. The intensity of the stray lightowing to surface or volume scattering in the center of the image of theobject is then at least 70% lower in comparison with the intensity ofthe stray light on account of the single reflections. If the edge lengthwere increased further, then although the separation of stray lightowing to surface or volume scattering from stray light on account ofsingle reflections would be better, the measurement signal for straylight on account of single reflections would then also decrease. If anobject having an edge length of 1.0 mm is not available, then themeasurement can also be carried out for an edge length of between 0.8 mmand 1.2 mm. Upon application of the proposed measures for reducing thesingle reflections on the lens surfaces of the second partial objective,the stray light intensity in the center of the image of the object isless than 1.1% in the stray light measurement with a square objecthaving the edge length of between 0.8 mm and 1.2 mm and in the case of apupil filling factor of between σ=0.2 and σ=0.3.

In one embodiment, the stray light intensity in the center of the imageof the object is less than 0.9% in the stray light measurement with asquare object having the edge length of between 0.8 mm and 1.2 mm and inthe case of a pupil filling factor of between σ=0.2 and σ=0.3.

In a further embodiment, the stray light intensity in the center of theimage of the object is less than 0.5% in the stray light measurementwith a square object having the edge length of between 0.8 mm and 1.2 mmand in the case of a pupil filling factor of between σ=0.2 and σ=0.3.

The contribution of the lens surfaces of the second partial objective tothe stray light can also be determined by measuring the stray light inthe image plane within the image field for two different pupil fillingfactors and by determining the variation of the stray light, since theformation of the single reflections is greatly dependent on the pupilfilling factor. Other causes of the stray light in the image plane suchas, for example, surface or volume scattering exhibit, by contrast, alow dependence on the pupil filling factor and lead to an almostillumination-independent background illumination in comparison withsingle reflections. The stray light measurement is therefore carriedout, for example, firstly by a pupil filling factor of σ=1.0 andsecondly for a pupil filling factor of σ=0.2. If the illumination systemof the projection exposure apparatus does not provide these fillingfactors, then a pupil filling factor of between σ=0.8 and σ=1.0 and,respectively, between σ=0.2 and σ=0.3 is used for the stray lightmeasurement. If the proposed measures for reducing the singlereflections are applied to the lens surfaces of the second partialobjective, then the maximum difference between the stray light intensityfor a pupil filling factor of between σ=0.2 and σ=0.3 and the straylight intensity for a pupil filling factor of between σ=0.8 and σ=1.0for an image point within the image field is less than 0.3%.

In one embodiment of the invention, the second partial objective has anabsolute value of the imaging scale of between 0.8 and 1.25. The secondpartial objective thus images the first intermediate image substantially1:1 onto the second intermediate image.

In one embodiment of the invention the concave mirror of the secondpartial objective is arranged in the region of a pupil plane, theposition of which results from the point of intersection of a paraxialprincipal ray with the optical axis of the projection objective. In thiscase, the concave mirror is arranged in the region of a pupil plane whenthe maximum height of all the principal rays emerging from the objectfield at the concave mirror is less than 20% of the diameter of theoptically utilized region of the concave mirror.

If the second partial objective has, on the one hand, an absolute valueof the imaging scale of between 0.8 and 1.25 and, on the other hand, aconcave mirror in the region of the pupil plane, then a substantiallysymmetrical construction results for the second partial objective inrelation to the concave mirror. If a lens surface at the second partialobjective then has no or only a small deviation from the marginal rayconcentricity, the stray light reflected at this lens surface generatesa stray light intermediate image which coincides at least approximatelywith the second intermediate image and is thus imaged into the imageplane by the third partial objective. This construction of the secondpartial objective which admittedly is favorable for the correction ofthe image field curvature and of chromatic aberrations, can lead,however, to single reflections that cannot be afforded tolerance. Thesingle reflections can then be reduced by the targeted deviation fromthe marginal ray concentricity at the lens surfaces or by covering thelens surfaces with the improved antireflection coating.

According to another aspect of the invention, the second intermediateimage is arranged in the region of the second folding mirror. In thiscase, the second intermediate image is arranged in the region of thesecond folding mirror when, in a fictitious plane which is arrangedperpendicular to the optical axis and which has the same point ofintersection with the optical axis as the second folding mirror, halfthe radial distance from the optical axis to that principal ray whichemerges from an object point within the object field with maximumdistance from the optical axis is greater than the radial distance ofthe marginal ray. The marginal ray already defined for determining themarginal ray concentricity is used in this case. As soon as a straylight intermediate image is not situated on the second intermediateimage in this case, the stray light beam is vignetted by the physicalboundary of the second folding mirror and the stray light intensity ofthis single reflection is reduced.

In a further aspect of the invention all the lenses in the secondpartial objective are arranged nearer to the concave mirror than to thefirst intermediate image or than to the second intermediate image. Sincethe lenses of the second partial objective are extended along theoptical axis, for determining the lens distance the midpoint between thetwo lens vertices is determined and the distance is measured from themidpoint. In this case, the position of the two intermediate imagesresults from the paraxial position of the intermediate images. By virtueof the lenses of the second partial objective being arranged nearer tothe concave mirror than to the intermediate images, they are alsofurther away from the second folding mirror. The greater the distance ofthe lens surfaces with respect to the second folding mirror, however,the greater the vignetting effect of the second folding mirror onaccount of the physical barrier thereof if the stray light intermediateimage does not ideally coincide with the second intermediate image.

In yet another aspect of the invention, the catadioptric projectionobjective is part of a projection exposure apparatus formicrolithography having, besides the projection objective, anillumination system for illuminating the object field in the objectplane.

In order to produce semiconductor components and other finely structuredcomponents with the projection exposure apparatus, provision is made fora reticle having a predetermined pattern in the object plane of thecatadioptric projection objective and for a wafer having alight-sensitive layer in the image plane of the catadioptric projectionobjective, the reticle is illuminated by the illumination system and,finally, the illuminated region of the reticle is imaged onto the waferby the catadioptric projection objective.

BRIEF DESCRIPTION OF THE DRAWINGS

Details and aspects of the invention are explained more specificallybelow on the basis of the exemplary embodiments illustrated in thefigures, in which:

FIG. 1 shows the lens section of a catadioptric projection objectivetogether with the projection light path;

FIG. 2 shows the lens section of the projection objective from FIG. 1together with a stray light path;

FIG. 3 shows a schematic illustration of an antireflection coating;

FIG. 4 shows a schematic illustration of an antireflection coating;

FIG. 5 shows a schematic illustration of an antireflection coating;

FIG. 6 shows a diagram with the reflectivity values of theantireflection coatings from FIGS. 3 to 5 as a function of the angles ofincidence;

FIG. 7 shows a stray light intensity distribution as a contour lineillustration for the pupil filling factor σ=0.2;

FIG. 8 shows stray light intensity profiles in the case ofantireflection coating of the lenses that are passed through twice inthe projection objective of FIG. 1 with a reflectivity of 0.2%;

FIG. 9 shows stray light intensity profiles in the case of anantireflection coating in accordance with FIG. 4 of the lenses that arepassed through twice in the projection objective of FIG. 1;

FIG. 10 shows a schematic illustration for illustrating the stray lightmeasurement technique;

FIG. 11 shows the lens section of a catadioptric projection objectivetogether with the projection light beam path;

FIG. 12 shows the lens section of the projection objective of FIG. 11with a stray light path;

FIG. 13 shows the lens section of the projection objective of FIG. 11with a stray light path;

FIG. 14 shows stray light intensity profiles in the case ofantireflection coating of the lenses that are passed through twice inthe projection objective of FIG. 11 with a reflectivity of 0.2%;

FIG. 15 shows stray light intensity profiles in the case of anantireflection coating in accordance with FIG. 4 of the lenses that arepassed through twice in the projection objective from FIG. 11;

FIG. 16 shows the lens section of a catadioptric projection objectivetogether with the projection light beam path;

FIG. 17 shows the lens section of a catadioptric projection objectivetogether with the projection light beam path; and

FIG. 18 shows a schematic illustration of a microlithography projectionexposure apparatus.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows the lens section of a catadioptric projection objective 1.The optical design of the projection objective 1 has been taken from thepatent application US2009/0092925A1 in the name of Omura, published on 9Apr. 2009, and corresponds to FIG. 4 therein. The optical data of thedesign are summarized in Table 1 in US2009/0092925A1. For a moredetailed description of the optical design of the projection objective1, therefore, reference is made to US2009/0092925A1, which is herebyincorporated into the present application by reference. The projectionobjective 1 images the object field 3 in the object plane 5 onto theimage field 7 in the image plane 9. It includes a first partialobjective 11, which images the object field 3 on to the first realintermediate image 13, the second partial objective 15, which images thefirst intermediate image 13 on to the second real intermediate image 17,and the third partial objective 19, which images the second intermediateimage 17 onto the image field 7. The second partial objective 15 isembodied as a catadioptric objective having the concave mirror 21 andthe two lenses L21 and L22. The folding mirror 23 is arranged in theregion of the first intermediate image 13, the folding mirror deflectingthe projection light 31 from the object plane 5 toward the concavemirror 21. The folding mirror 25 is arranged in the region of the secondintermediate image 17, this folding mirror deflecting the projectionlight from the concave mirror 21 toward the image plane 9.

A stray light analysis was carried out for the projection objective 1 inorder to determine the stray light paths on which the stray light canpass into the image plane 9 as single, double or multiple reflection andlead to a background illumination there. FIG. 2 shows for the projectionobjective 1 such a stray light path 33 arising from the fact that theprojection light 31 is reflected at that surface of the lens L21 whichfaces the concave mirror 21, the surface being referred to hereinafteras back surface of the lens L21. In the stray light path 33 illustrated,the stray light 33, deviating from the projection light path 31, doesnot pass through the lens L22 and the concave mirror 21, but passesthrough all further optical surfaces which the projection light 31 wouldalso pass through if the projection light 31 entered into the lens L21again after reflection at the concave mirror 21 and after passingthrough the lens L22. In the stray light path 33, the stray lightintermediate image 35 arises in the region of the folding mirror 25 andtherefore simultaneously also virtually at a location of the secondintermediate image 17. As a result, virtually the entire stray light isreflected at the second folding mirror 25 without being vignetted by thephysical boundary of the folding mirror 25, and, in a manner similar tothe projection light 31, passes through the third partial objective 19as far as the image plane 9. The aperture stop 29 is virtuallycompletely illuminated by the stray light, such that it is also notpossible to filter out the stray light with a spatially delimiteddiaphragm in the region of the aperture stop plane without theprojection light 31 being significantly vignetted.

The back surface of the lens L21 consequently produces a singlereflection with very high stray light intensity. In this case, the straylight intensity corresponds approximately to the intensity of theprojection light multiplied by the reflectivity of the back surface ofthe lens L21. This strong single reflection arises because the backsurface of the lens L21 has a marginal ray concentricity of 0.6°.Therefore, virtually marginal ray concentricity is provided. Togetherwith the fact that the second partial objective 15 has an absolute valueof the imaging scale of 1.03 and the concave mirror 21 is arranged inthe region of a pupil plane, the stray light intermediate image 35 isthereby generated virtually at the location of the second intermediateimage 17 and the stray light 33 is thus transmitted almost completelyvia the second folding mirror 25.

The front surface of the lens L21, with a value of 15.9°, likewise has alow marginal ray concentricity, with the result that this surface alsomakes a contribution to the stray light in the image plane 9. Themarginal ray concentricity of the back surface of the lens L22, whichfaces the concave mirror 21, is 24.0°, and the marginal rayconcentricity of the front surface of the lens L22 is 22.9°, with theresult that although these two surfaces likewise contribute to the straylight in the image plane 9, the magnitude of their contribution fallsfar short of that of the back surface of the lens L21. Very generally,the lenses L21 and L22 of the second partial objective 15 should beregarded as susceptible to stray light since both lenses are lenseswhich are passed through twice and through which the projection light 31passes both on the light path toward the concave mirror 21 and on thelight path away from the concave mirror 21. As soon as a stray light rayreflected at the lens surfaces of these lenses L21 and L22 that arepassed through twice passes through the second folding mirror 25, thereis the possibility of such a stray light ray reaching the image plane 9and contributing to the extraneous light. This is a fundamental problemof this class of projection objectives.

In the case of single reflections, the intensity of the stray light inthe image plane 9 is linearly dependent on the reflectivity of that lenssurface at which the stray light is reflected. The lens surfaces of thelenses L21 and L22 that are passed through twice in the projectionobjective 1 are covered therefore with an antireflection coating havinga reflectivity of less than 0.2% for the projection light wavelength of193.3 nm and for an angle of incidence range of between 0° and 30°.FIGS. 3 to 5 illustrate various exemplary embodiments of such anantireflection coating.

FIG. 3 shows in a schematic illustration the layer sequence of theantireflection coating 337 proceeding from the substrate 339 of thelens, this substrate being composed of quartz (SiO₂). The antireflectioncoating 337 includes six layers composed alternately of material havinghigh refractive index and material having a low refractive index.Magnesium fluoride (MgF₂) is used as material having a low refractiveindex. Lanthanum fluoride (LaF₃) is used as material having a highrefractive index. The geometrical thicknesses of the individual layers,the materials and the refractive indices thereof and also the referencesigns used in FIG. 3 are indicated in table 1. The thicknesses of theindividual layers are illustrated correctly relative to one another inFIG. 3.

TABLE 1 Reference symbol Thickness [nm] Material Refractive index 339Substrate SiO₂ 1.56 341 21.568 LaF₃ 1.69 343 67.626 MgF₂ 1.42 345 29.775LaF₃ 1.69 347 42.969 MgF₂ 1.42 349 34.261 LaF₃ 1.69 351 26.823 MgF₂ 1.42

FIG. 4 shows an embodiment of an antireflection coating 437, in turnhaving six layers composed alternately of material having a highrefractive index and material having a low refractive index. MgF₂ isused as material having a low refractive index, and LaF₃ is used asmaterial having a high refractive index. The thicknesses of theindividual layers, the materials and the refractive indices thereof andalso the reference signs used in FIG. 4 are compiled in table 2.

TABLE 2 Reference symbol Thickness [nm] Material Refractive index 439Substrate SiO₂ 1.56 441 13.762 LaF₃ 1.69 443 69.414 MgF₂ 1.42 445 42.945LaF₃ 1.69 447 16.440 MgF₂ 1.42 449 40.914 LaF₃ 1.69 451 30.145 MgF₂ 1.42

FIG. 5 shows an exemplary embodiment of an antireflection coating 537,including seven layers composed alternately of material having a highrefractive index and material having a low refractive index. MgF₂ isused as material having a low refractive index, and LaF₃ is used asmaterial having a high refractive index. The thicknesses of theindividual layers, the materials and the refractive indices thereof andalso the reference signs used in FIG. 5 are compiled in table 3.

TABLE 3 Reference symbol Thickness [nm] Material Refractive index 539Substrate SiO₂ 1.56 541 37.738 MgF₂ 1.42 543 15.378 LaF₃ 1.69 545 9.098MgF₂ 1.42 547 29.126 LaF₃ 1.69 549 36.117 MgF₂ 1.42 551 29.917 LaF₃ 1.69553 33.958 MgF₂ 1.42

FIG. 6 shows, for the antireflection coatings 337, 437 and 537illustrated in FIGS. 3 to 5, the reflectivity values in the unit [%] asa function of the angles of incidence in the unit [°]. The dash-dottedreflectivity curve 655 results for the antireflection coating 337 havingthe layer construction in accordance with table 1, the solidreflectivity curve 657 results for the antireflection coating 437 havingthe layer construction in accordance with table 2 and the dashedreflectivity curve 659 results for the antireflection coating 537 havingthe layer construction in accordance with table 3. In the case of allthree antireflection coatings, the reflectivity curves 655, 657 and 659for the angle of incidence range of 0° to 30° run below a reflectivityvalue of 0.2%, even below a reflectivity value of 0.1%. Up to an angleof incidence of 20°, the reflectivity curves 655, 657 and 659 run belowa reflectivity value of 0.1%, even below a reflectivity value of 0.05%.In the case of the antireflection coatings 337 and 537, the reflectivitycurves 655 and 659 for an angle of incidence range of 0° to 10° even runbelow a reflectivity value of 0.02%.

Using suitable ray tracing programs, for a given optical design of aprojection objective, it is possible to calculate the intensitydistribution of the stray light in the image plane taking account of theantireflection coatings. FIG. 7 shows for the projection objective 1 theintensity distribution 761 of the stray light in the image plane 9 in acontour line illustration. The contour lines are illustrated with aspacing of 0.1%. In this case, the stray light intensity relates to thehomogeneous ambient brightness in the image field. In the simulation,the object field 3 was illuminated homogeneously with a pupil fillingfactor of σ=0.2. In this case, exclusively the single reflections at thelens surfaces of the lenses L21 and L22 that are passed through twice inthe second partial objective 15 are taken into account as stray light.In this case, the lens surfaces are covered with an antireflectioncoating having a reflectivity of 0.2% for all angles of incidence.Antireflection coatings such as are used for reducing double reflectionsor higher-order reflections have this reflectivity value. A reflectivityof 0.2% is sufficient for avoiding double reflections since such areflection, on account of the two reflections, has an intensity of just0.2%·0.2%=0.0004%. The contour line illustration makes it clear,however, that such an antireflection coating does not effectivelysuppress the formation of disturbing single reflections. The singlereflections completely illuminate the image field 763 which is depictedusing dashed lines, and over the entire image field lead to a backgroundillumination of at least 0.4%, in extensive regions even above 0.8%. Theextent of the stray light in the image plane 9 (this extent beingcomparable with the extent of the image field 7) is caused by the factthat the stray light image of the object field 3 is situated more orless in the image plane 9, as becomes clear in FIG. 2 for the singlereflection at the back surface of the lens L21.

FIG. 8 shows a section through the intensity distribution 761 along theline 765, running in the longitudinal direction of the image field 7through the center of the image field 7, as intensity profile 867. Themaximum stray light intensity is 0.93% in the image center and 0.41% atthe image edge at x=±13 mm. The stray light simulation was carried outnot only with an illumination with the pupil filling factor of σ=0.2 butalso with a pupil filling factor of σ=1.0, that is to say with completeillumination of the entrance pupil of the projection objective. Thesection through the stray light intensity distribution for a pupilfilling factor of σ=1.0 along the line 765 is illustrated in dashedfashion as intensity profile 869 in FIG. 8. With complete illuminationof the entrance pupil of the projection objective, the maximum straylight intensity is 0.40%. Within the image field 7, the stray lightintensity has a virtually constant value. It is evident that the straylight intensity is greatly dependent on the pupil filling factor. Thus,the maximum stray light intensity within the image field 7 for a pupilfilling factor of σ=1.0 is lower by 0.523% than that for a pupil fillingfactor of σ=0.2. This is characteristic of stray light caused by singlereflections. Although stray light on account of surface or a volumescattering likewise leads to a background illumination in the entireimage field, the intensity distribution thereof is virtually independentof the pupil filling factor in the image plane in comparison with singlereflections. If the measured stray light, as in the present case, has agreat dependence on the pupil filling factor, then this is an indicationof the formation of single reflections.

FIG. 9 shows the intensity profile 971 for a pupil filling factor ofσ=0.2 and the intensity profile 973 for the pupil filling factor ofσ=1.0 as sections through stray light intensity distributions, whicharise if the lens surfaces of the second partial objective are coveredwith the antireflection coating 437, the layer construction of which isindicated in table 2. With the improved antireflection coating themaximum stray light intensity within the image field 7 decreases from0.93% to 0.02% for the pupil filling factor of σ=0.2, and from 0.40% to0.01% for the pupil filling factor of σ=1.0. It should be taken intoconsideration that in FIG. 9 the scale of the intensity axis is reducedby a factor of 10 in comparison with the scale in FIG. 8. For theimproved antireflection coating the maximum variation of the stray lightbetween the two pupil filling factors is just 0.01% and is thereforevanishingly small. The single reflections can thus be effectivelysuppressed with the improved antireflection coating 437. By thereforemeasuring the stray light intensity once for the pupil filling factor ofσ=0.2 and once for the pupil filling factor of σ=1.0 within the imagefield 7, it is possible to determine the influence of the singlereflections of the lenses that are passed through twice in the secondpartial objective 15 independently of further contributions to the straylight which have other causes and are not dependent on the pupil factorchosen.

In order to measure the stray light in the image plane, the so-calledKirk test is employed, for example, which is described inUS2009/0086179A1, inter alia. In the Kirk test, a square object whichhas a predetermined edge length, for example, 1.0 mm and is itself notluminous is arranged within the object field 3. The object used is asmall box, for example, which completely absorbs the illumination lightand therefore can be regarded as “black”. By contrast, the surroundingsof the small box are homogeneously illuminated by the illuminationlight. The small box is imaged into the image plane 9 by the projectionobjective 1. In the case of ideal imaging and disregarding stray light,a square, unilluminated region would arise in the image plane 9. FIG. 10shows in schematic illustration, a section through the intensity profilein the region of the image of the small box. In the case of idealimaging and disregarding the stray light, the intensity curve 1075,depicted by a dashed line, arises, which falls abruptly from 100% to 0%in the region of the image of the small box. The stray light has theeffect, however, that it is not dark in the center 1081 of the image ofthe small box, rather a stray light intensity can be detected. Theintensity curve 1077, illustrated by a solid line, illustrates theintensity profile which arises upon taking account of the singlereflections at the lens surfaces of the second partial objective 15.Stray light on account of surface or volume scattering leads to theintensity profile 1079 illustrated in dash-dotted fashion, which leadsto a significantly lower stray light intensity in the center of theimage of the small box given a sufficient edge length of the small box.By virtue of the edge length of the small box being 1.0 mm, during themeasurement of the stray light it is possible to distinguish thecontribution of the lens surfaces of the second partial objective 15from other stray light contributions. In this case, the intensity valuein the center 1081 of the image of the small box corresponds to theintegrated stray light intensity which results from stray light sourcesarranged outside the small box.

For a pupil filling factor of σ=0.2 and for a small box having the edgelength of 1.0 mm, an intensity of 1.1% arises in the center of the imageof the small box if all the lens surfaces of the partial objective 15are covered with an antireflection coating having a reflectivity of 0.2%for all angles of incidence. If, by contrast, the lens surfaces of thelenses L21 and L22 are covered with the antireflection coating 437indicated in table 2, then the stray light intensity in the center ofthe image of the small box decreases to 0.3%. The measurement of thestray light according to the Kirk test using a square small box havingan edge length of between 0.8 mm and 1.2 mm thus makes it possible todirectly determine the stray light proportion owing to singlereflections.

FIG. 11 shows a lens section of a catadioptric projection objective1101. The elements in FIG. 11, which correspond to the elements fromFIG. 1, have the same reference signs as in FIG. 1 increased by thenumber 1100; for a description of these elements, reference is made tothe description concerning FIG. 1.

The optical data for the projection objective 1101 are compiled in table4. The aspherical surfaces can be described by the following sagittaformula:

${p(h)} = {\frac{\frac{1}{R}h^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)\left( \frac{1}{R} \right)^{2}h^{2}}}} + {\sum\limits_{k = 1}\;{C_{k}h^{{2\; k} + 2}}}}$

In this case, p represents the axial distance in [mm] of the asphericalsurface from a plane—perpendicular to the optical axis—through thevertex of the aspherical surface in the case of radial distance h in[mm], R represents the vertex radius in [mm], K represents the conicalconstant, and Ck represents the individual aspherical constants of theorder k in

$\frac{1}{\left\lbrack {mm}^{{2\; k} + 2} \right\rbrack}.$

The projection objective 1101 has a numerical aperture of NA=1.2 in theimage plane 1109. The operating wavelength is 193.306 nm. The imagefield 1107 amounts to 26.0 mm×5.5 mm and has a minimum distance from theoptical axis 1127 of 1.98 mm. The projection objective 1101 has anabsolute value of the imaging scale of 0.25. This present embodimentinvolves an immersion projection objective, in which during operationwater as immersion liquid is situated between the last lens surface andthe object to be exposed.

The first partial objective 1111 is formed by the surfaces 1 to 20, thesecond partial objective 1115 is formed by the surfaces 22 to 26 and thethird partial objective 1119 is formed by the surfaces 28 to 52. Thefolding mirrors 1123 and 1125 with the surface numbers 21 and 27 are notassigned to any of the three partial objectives 1111, 1115 and 1119,since the folding mirrors 1123 and 1125, as plane mirrors have noinfluence on the imaging, but rather only deflect the projection light1131. The first partial objective 1111 has an absolute value of theimaging scale of 1.05, the second partial objective 1115 has an absolutevalue of the imaging scale of 1.01 and the third partial objective 1119has an absolute value of the imaging scale of 0.23.

All the principal rays which emerge from the object field 1103 and whichintersect the optical axis 1127 at the location of the aperturediaphragm 1129 have at the concave mirror 1121 a height which is lessthan 9.1% of the diameter of the optically utilized region of theconcave mirror 1121. The concave mirror 1121 is thus arranged in theregion of a pupil plane of the projection objective 1101.

The principal ray emerging from the object point (x=52.00 mm, y=29.93mm) has a radial distance from the optical axis of 70 mm in a fictitiousplane which is perpendicular to the optical axis 1127 and whichintersects the optical axis 1127 at the same location as the secondfolding mirror 1125. The fictitious marginal ray has, by contrast,nearly a radial distance of 1.5 mm in this plane. In this case, theobject point (x=52.00 mm, y=29.93 mm) has the largest distance from theoptical axis 1127 within the object field 1103. The second intermediateimage 1117 is thus arranged in the region of the second folding mirror1125.

The sequence of the lens surfaces in table 4 corresponds to theprojection light path. The projection light passes through all thesurfaces in the order indicated. The lens L1111 of the second partialobjective 1115 is passed through twice and is therefore indicated twicewith the surface numbers 22 and 23, and 26 and 25, in table 4. In thiscase, the lens L1111 is the sole lens in the second partial objective1115. The distance between the lens L1111 and the concave mirror 1121 is40.2 mm. The first paraxial intermediate image has a distance of 312.12mm from the concave mirror 1121, the second paraxial intermediate imagehas a distance of 316.25 mm from the concave mirror 1121. The lens L1111is therefore arranged nearer to the concave mirror 1121 than to thefirst intermediate image 1113 or to the second intermediate image 1117.

In principle, the lens L1111, owing to its arrangement in the secondpartial objective as a lens that is passed through twice, would becritical for the production of a single reflection in the image plane1109. However, that lens surface of the lens L1111 which faces theconcave mirror 1121, that is to say the back surface of the lens L1111,has a marginal ray concentricity of 30.0°, and the front surface has amarginal ray concentricity of 30.8°. Both surfaces thus deviateconsiderably from the marginal ray concentricity. At the same time, theextent of the second folding mirror 1125 is adapted to the extent of theprojection light beam 1131. Thus, the extent of the projection lightbeam on the second folding mirror 1125 is 141.1 mm×65.4 mm, while thesecond folding mirror 1125 has an extent of 145 mm×70 mm. The formationof a single reflection is largely suppressed on account of the deviationof the two lens surfaces of the lens L1111 from the marginal rayconcentricity and the second folding mirror 1125 adapted to the extentof the projection light beam.

FIG. 12 shows, for the exemplary embodiment from FIG. 11, the straylight path 1233, formed if the projection light 1131 is reflected at theback surface of the lens L1111. It becomes clear from the stray lightpath 1233 that the stray light intermediate image 1235 is not formed onthe second folding mirror 1125, but rather far away from the foldingmirror 1125 in the vicinity of the aperture stop plane with the aperturestop 1129. The stray light beam at the second folding mirror 1125 thushas a much larger extent than the second folding mirror 1125 and islargely vignetted. Consequently, the stray light beam in the objectplane 1105 has only a small aperture in comparison with the maximumpossible aperture. In addition, this stray light is greatly focused inthe region of the aperture stop 1129, such that it could be shaded by adiaphragm around the optical axis.

FIG. 13 shows, for the exemplary embodiment from FIG. 11, the straylight path 1333 formed if the projection light 1131 is reflected at thefront surface of the lens L1111. In this case, the stray lightintermediate image 1335 is formed shortly after the lens L1111 and thuslikewise far away from the folding mirror 1125 such that the stray lightbeam at the second folding mirror 1125 has a much larger extent than thesecond folding mirror 1125 and is largely vignetted.

By virtue of the front and back surfaces of the lens L1111 deviatingmore than 20° from the marginal ray concentricity, the formation of asingle reflection in the image plane 1109 can be largely suppressed.

In order to show the reduction of the single reflections by the specificconfiguration of the lens surfaces of the second partial objective 1115,stray light simulations were carried out for the projection objective1101 and the stray light intensity distributions in the image plane 1109were determined. In the simulation, the object field 1103 washomogeneously illuminated firstly with a pupil filling factor of σ=0.2and secondly with a pupil filling factor of σ=1.0. In this case,exclusively the single reflections at the lens surfaces of the lensL1111 that is passed through twice in the second partial objective 1115are taken into account as stray light. In this case, the lens surfacesare covered with an antireflection coating having a reflectivity of 0.2%for all angles of incidence. FIG. 14 shows, with the intensity profile1483, a section through the stray light intensity distribution for thepupil filling factor of σ=0.2 along a line running in the longitudinaldirection of the image field 1107 through the center of the image field1107. The maximum stray light intensity is 0.18% in the image center and0.13% at the image edge at x=±13 mm. The section through the stray lightintensity distribution for a pupil filling factor of σ=1.0 isillustrated as intensity profile 1485 in FIG. 14. The maximum straylight intensity is just 0.01% with complete illumination of the entrancepupil of the projection objective. Although a dependence of the straylight on the pupil filling factor is still evident, the variationbetween a pupil filling factor of σ=1.0 and a pupil filling factor ofσ=0.2 is only 0.17%.

FIG. 15 shows the intensity profile 1487 for a pupil filling factor ofσ=0.2 and the intensity profile 1489 for the pupil filling factor ofσ=1.0 as sections through stray light intensity distributions, whicharise if the lens surfaces of the second partial objective are coveredwith the antireflection coating 437, the layer construction of which isindicated in table 2. With the improved antireflection coating, themaximum stray light intensity within the image field 1107 decreases from0.18% to 0.004% for the pupil filling factor of 6=0.2 and from 0.01% to0.002% for the pupil filling factor of σ=1.0. It should be taken intoconsideration that in FIG. 15 the scale of the intensity axis has onceagain been reduced by a factor of 10 in comparison with the scale inFIG. 14. Consequently, the single reflection is practically no longerdetectable.

If the Kirk test is employed using a square small box having an edgelength of 1.0 mm, an intensity of 0.4% results for a pupil fillingfactor of σ=0.2 in the center of the image of the small box if all thelens surfaces of the partial objective 1115 are covered with anantireflection coating having a reflectivity of 0.2% for all angles ofincidence. If, by contrast, the lens surfaces of the lens L1111 arecovered with the antireflection coating 437 indicated in table 2, thenthe stray light intensity in the center of the image of the small boxdecreases to 0.3%.

FIG. 16 shows a lens section of a catadioptric projection objective1601. The elements in FIG. 16 which correspond to the elements from FIG.1 have the same reference signs as in FIG. 1 increased by the number1600; for a description of these elements reference is made to thedescription of FIG. 1.

The optical data for the projection objective 1601 are compiled in table5. The projection objective 1601 has a numerical aperture of NA=1.2 inthe image plane 1609. The operating wavelength is 193.306 nm. The imagefield 1607 is 26 mm×5.5 mm and has a minimum distance from the opticalaxis 1627 of 1.98 mm. The projection objective 1601 has an absolutevalue of the imaging scale of 0.25. The present embodiment againinvolves an immersion projection objective, in which during theoperation water as immersion liquid is situated between the last lenssurface and the object to be exposed.

The first partial objective 1611 is formed by the surfaces 1 to 20, thesecond partial objective 1615 is formed by the surfaces 22 to 26 and thethird partial objective 1619 is formed by the surfaces 28 to 52. Thefirst partial objective 1611 has an absolute value of the imaging scaleof 1.03, the second partial objective 1615 has an absolute value of theimaging scale of 1.01 and the third partial objective 1619 has anabsolute value of the imaging scale of 0.24.

All the principal rays which emerge from the object field 1603 and whichintersect the optical axis 1627 at the location of the aperturediaphragm 1629 have at the concave mirror 1621, a height which is lessthan 8.6% of the diameter of the optically utilized region of theconcave mirror 1621. The concave mirror 1621 is thus arranged in theregion of a pupil plane of the projection objective 1601.

The principal ray emerging from the object point (x=52 mm, y=29.93 mm)has a radial distance of 68.29 mm in a fictitious plane which isperpendicular to the axis 1627 and which intersects the optical axis1627 at the same location as the second folding mirror 1625. Bycontrast, the fictitious marginal ray has only a radial distance of 0.82mm in this plane. In this case, the object point (x=52 mm, y=29.93 mm)has the largest distance from the optical axis 1627 within the objectfield 1603. The second intermediate image 1617 is thus arranged in theregion of the second folding mirror 1625.

The lens L1611 is the sole lens in the second partial objective 1615.Both the front surface and the back surface of the lens L1611 areconfigured as aspherical surfaces. The distance between the lens L1611and the concave mirror 1621 is 40.2 mm. The first paraxial intermediateimage has a distance of 300.48 mm from the concave mirror 1621, thesecond paraxial intermediate image has a distance of 316.25 mm from theconcave mirror 1621. The lens L1611 is thus arranged nearer to theconcave mirror 1621 than to the first intermediate image 1613 or to thesecond intermediate image 1617.

That lens surface of the lens L1611 which faces the concave mirror 1621,that is to say the back surface of the lens L1611, has a marginal rayconcentricity of 30.9°, and the front surface has a marginal rayconcentricity of 30.2°. Both surfaces thus deviate considerably from themarginal ray concentricity.

FIG. 17 shows a lens section of a catadioptric projection objective1701. The elements in FIG. 17 which correspond to the elements from FIG.1 have the same reference signs as in FIG. 1 increased by the number1700; for a description of these elements reference is made to thedescription of FIG. 1, above.

The optical data for the projection objective 1701 are compiled in table6. The projection objective 1701 has a numerical aperture of NA=1.2 inthe image plane 1709. The operating wavelength is 193.307 nm. The imagefield 1707 is 26.0 mm×5.5 mm and has a minimum distance from the opticalaxis 1727 of 1.98 mm. The projection objective 1701 has an absolutevalue of the imaging scale of 0.25. The present embodiment is again animmersion projection objective, in which during the operation water asimmersion liquid is situated between the last lens surface and theobject to be exposed.

The first partial objective 1711 is formed by the surfaces 1 to 22, thesecond partial objective 1715 is formed by the surfaces 24 to 28 and thethird partial objective 1719 is formed by the surfaces 30 to 58. Thefirst partial objective 1711 has an absolute value of the imaging scaleof 0.96, the second partial objective 1715 has an absolute value of theimaging scale of 1.00 and the third partial objective 1719 has anabsolute value of the imaging scale of 0.26.

All the principal rays which emerge from the object field 1703 and whichintersect the optical axis 1727 at the location of the aperturediaphragm 1729 have at the concave mirror 1721, a height which is lessthan 7.5% of the diameter of the optically utilized region of theconcave mirror 1721. The concave mirror 1721 is thus arranged in theregion of a pupil plane of the projection objective 1701.

The principal ray emerging from the object point (x=52 mm, y=29.93 mm)has a radial distance of 67.77 mm in a fictitious plane which isperpendicular to the axis 1727 and which intersects the optical axis1727 at the same location as the second folding mirror 1725. Bycontrast, the fictitious marginal ray has only a radial distance of 1.27mm in this plane. In this case, the object point (x=52 mm, y=29.93 mm)has the largest distance from the optical axis 1727 within the objectfield 1703. The second intermediate image 1717 is thus arranged in theregion of the second folding mirror 1725.

The lens L1712 is the sole lens in the second partial objective 1715.Both the front surface and the back surface of the lens L1712 areconfigured as aspherical surfaces. The distance between the lens L1712and the concave mirror 1721 is 33.4 mm. The first paraxial intermediateimage has a distance of 188.92 mm from the concave mirror 1721, thesecond paraxial intermediate image has a distance of 189.59 mm from theconcave mirror 1721. The lens L1712 is thus arranged nearer to theconcave mirror 1721 than to the first intermediate image 1713 or to thesecond intermediate image 1717.

That lens surface of the lens L1712 which faces the concave mirror 1721,that is to say the back surface of the lens L1712, has a marginal rayconcentricity of 38.6°, and the front surface has a marginal rayconcentricity of 20.0°. Both surfaces thus deviate from the marginal rayconcentricity. In comparison with the lenses L1111 in the projectionobjectives 1101 and L1611 in the projection objective 1601, the lensbending of the lens L1712 is opposite to that of the lenses L1111 orL1611. While in the case of the front surfaces of the lenses L1111 orL1611 the surface normal at the intersection point of the fictitiousmarginal ray run between marginal ray and optical axis 1127 and 1627,respectively, in the case of the front surface of the lens L1712 thefictitious marginal ray runs between surface normal at the intersectionpoint of the marginal ray and the optical axis 1727. Consequently, thefront surface of the lens L1712 is convexly curved with respect to themarginal ray incident from the first intermediate image 1713.

FIG. 18 schematically shows a projection exposure apparatus 1801 formicrolithography that serves for producing semiconductor components orother finely structured components. The projection exposure apparatus1801 has an excimer laser 1803 as light source having an operatingwavelength of 193 nm, although other excimer lasers for example havingoperating wavelengths of 157 nm or 248 nm are also possible. Anillumination system 1805, disposed downstream of the laser, generates asharply bounded, homogeneously illuminated illumination field that issimultaneously adapted with regard to its angular distribution to therequirements of the projection objective 1813, disposed downstream ofthe illumination system. The illumination system 1805 has devices forselecting the illumination mode and can thereby generate for example inthe exit pupil of the illumination system 1805, or in the entrance pupilof the projection objective 1813, a conventional illumination with avariable pupil filling factor σ, an annular illumination, dipoleillumination or quadrupole illumination.

A device 1809 for holding and manipulating a reticle 1807 is arranged inthe light direction downstream of the illumination system 1805. Thereticle 1807, also referred to as a mask, has the structure to beimaged. The device 1809 is used to move the reticle 1807 in a scanningdirection for scanning purposes in the object plane 1811.

The projection objective 1813 is a catadioptric projection objective, asdescribed with reference to FIGS. 1, 11, 16 and 17. The catadioptricprojection objective 1813 images that part of the reticle 1807 which isilluminated by the illumination system 1805 onto the wafer 1815 indemagnified fashion. The wafer 1815 has a light-sensitive layer that isexposed upon irradiation with the projection light.

The wafer 1815 is held by a device 1819 that permits a correspondingmovement of the wafer 1815 synchronized with the scanning movement ofthe reticle. The device 1819 also has manipulators that position thewafer 1815 optimally in the image plane 1817 of the projection objective1813. The device 1819 is designed for the immersion use of theprojection objective. It has a holding unit 1821 having a shallowdepression or recess for holding the wafer 1815. The holding unit 1821has a peripheral edge 1823 in order to prevent the immersion medium 1825from flowing away.

The projection exposure apparatus is controlled by a central computerunit 1827.

In order to produce semiconductor components and other finely structuredcomponents with the projection exposure apparatus 1801, therefore,provision is made of a reticle 1807 having a predetermined pattern inthe object plane 1811 of the catadioptric projection objective 1813,provision is made of a wafer 1815 having a light-sensitive layer in theimage plane of the catadioptric projection objective 1813, the reticle1807 is illuminated with the illumination system 1805 and, finally, theilluminated region of the reticle 1807 is imaged onto the wafer 1815 bythe catadioptric projection objective 1813.

The above description of the preferred embodiments has been given by wayof example. From the disclosure given, those skilled in the art will notonly understand the present invention and its attendant advantages, butwill also find apparent various changes and modifications to thestructures and methods disclosed. The applicant seeks, therefore, tocover all such changes and modifications as fall within the spirit andscope of the invention, as defined by the appended claims, andequivalents thereof.

TABLE 4 NA 1.2 Object height 60 Wavelength 193.306 Surface RadiusThickness Material Refractive index Half diameter 0 0.000000 50.00000060.0 1 0.000000 8.000000 SiO2 1.560326 75.8 2 0.000000 59.610620 77.4 31439.380884 32.013517 SiO2 1.560326 97.3 4 −271.207483 2.110453 99.0 5583.614042 16.197420 SiO2 1.560326 100.5 6 1991.428343 3.396948 100.2 7137.148931 46.192632 SiO2 1.560326 99.4 8 1990.872673 35.955682 95.9 971.140440 46.083036 SiO2 1.560326 64.8 10 74.802466 57.285100 47.1 11−67.442491 36.623983 SiO2 1.560326 45.5 12 −120.009774 0.999896 67.8 13−316.440706 21.841425 SiO2 1.560326 76.2 14 −166.255801 36.560578 81.215 −182.509454 38.166255 SiO2 1.560326 94.7 16 −116.928613 0.999888100.2 17 2344.762362 37.265639 SiO2 1.560326 108.4 18 −253.1200360.999878 109.2 19 208.087128 40.064181 SiO2 1.560326 102.3 20−744.545556 61.091342 99.6 21 0.000000 −287.184726 Mirror 70.8 22100.735080 −15.000002 SiO2 1.560326 77.3 23 1546.908367 −32.735719 95.324 154.868408 32.735719 Mirror 97.4 25 1546.908367 15.000002 SiO21.560326 95.3 26 100.735080 287.184726 77.3 27 0.000000 −67.470410Mirror 71.5 28 1166.218905 −26.117540 SiO2 1.560326 89.9 29 228.675901−0.999977 92.6 30 −229.673150 −62.112757 SiO2 1.560326 102.2 311651.573796 −4.139282 101.4 32 −168.631918 −115.053946 SiO2 1.56032698.5 33 −494.607195 −10.890377 72.1 34 −2693.637221 −9.999917 SiO21.560326 71.0 35 −182.034682 −26.163167 66.3 36 458.881180 −9.999883SiO2 1.560326 66.6 37 −150.000000 −53.839743 70.5 38 116.341201−37.590742 SiO2 1.560326 73.3 39 158.311181 −1.000526 96.0 40 540.901698−31.553546 SiO2 1.560326 112.9 41 236.220218 −0.999904 117.3 42−344.717958 −65.184212 SiO2 1.560326 139.6 43 282.807945 −3.863222 140.044 −254.540028 −48.998341 SiO2 1.560326 136.3 45 13988.972761 −24.472967133.8 46 0.000000 10.645713 124.2 47 −159.621355 −50.079617 SiO21.560326 115.6 48 −320.728784 −20.982865 106.5 49 −125.755069 −48.738034SiO2 1.560326 87.2 50 −767.843186 −0.999622 74.0 51 −57.414214−57.012850 SiO2 1.560326 50.1 52 0.000000 −1.000000 H2O 1.470000 16.4 530.000000 0.000000 Aspherical Constants Surface 8 15 20 23 25 K 0 0 0 0 0C1 6.212168E−08 −2.065631E−08 3.954655E−08 4.109750E−08 4.109750E−08 C2−2.284725E−12 1.154467E−12 −1.975939E−13 −2.014598E−12 −2.014598E−12 C34.919789E−17 −1.754944E−16 −2.888308E−17 1.434330E−16 1.434330E−16 C41.170467E−20 −1.439257E−21 1.773508E−21 −1.120664E−20 −1.120664E−20 C5−1.050170E−24 4.255683E−25 −5.791298E−26 6.611410E−25 6.611410E−25 C62.860117E−29 −2.463045E−29 9.438651E−31 −1.801493E−29 −1.801493E−29Surface 33 35 37 40 43 K 0 0 0 0 0 C1 −8.304509E−08 −1.571447E−071.854475E−07 5.368234E−09 −2.403621E−08 C2 3.027151E−12 −1.893541E−111.105850E−11 −9.295068E−13 −1.650116E−13 C3 −1.487997E−15 2.354878E−15−3.337902E−15 −4.764400E−17 −1.675626E−17 C4 1.391498E−19 −3.277504E−195.695337E−19 −6.981458E−22 7.042709E−22 C5 −5.936943E−24 3.740597E−24−5.380116E−23 5.210284E−26 −7.079479E−27 C6 −3.355570E−28 3.816347E−272.436028E−27 1.403914E−30 −9.754026E−32 Surface 48 50 K 0 0 C13.410190E−08 −1.004308E−07 C2 −6.659776E−12 4.830886E−12 C3 4.814964E−16−1.220533E−15 C4 −2.364870E−20 1.499788E−19 C5 7.232487E−25−1.105452E−23 C6 −9.143981E−30 2.727683E−28 Decentering and tilt SurfaceΔx Δy Δz alpha beta 21 0 0 0 45 0 27 0 0 0 45 0

TABLE 5 NA 1.2 Object height 60 Wavelength 193.306 Surface RadiusThickness Material Refractive index Half diameter 0 0.000000 50.00000060.0 1 0.000000 8.000000 SiO2 1.560326 75.8 2 0.000000 52.869064 77.4 31151.891547 30.208455 SiO2 1.560326 95.4 4 −297.772920 3.256949 97.0 5392.306364 20.384062 SiO2 1.560326 99.2 6 2065.429234 7.942304 98.7 7127.761865 45.517258 SiO2 1.560326 96.0 8 969.751914 34.534602 92.1 972.468670 38.613055 SiO2 1.560326 62.1 10 73.543725 56.553595 46.3 11−68.108298 31.573318 SiO2 1.560326 46.0 12 −109.674176 0.999866 65.2 13−328.152276 23.012797 SiO2 1.560326 74.4 14 −156.396340 49.715086 79.215 −201.140848 38.713984 SiO2 1.560326 98.1 16 −122.640971 0.999882103.2 17 2881.906041 35.379085 SiO2 1.560326 109.1 18 −269.8894740.999898 109.8 19 201.477991 40.395129 SiO2 1.560326 102.2 20−820.910555 64.207152 99.4 21 0.000000 −272.609099 Mirror 68.5 2295.391786 −15.000002 SiO2 1.560326 75.6 23 1195.870422 −32.735719 93.624 150.428374 32.735719 Mirror 95.7 25 1195.870422 15.000002 SiO21.560326 93.6 26 95.391786 272.609099 75.6 27 0.000000 −66.033144 Mirror69.5 28 1947.063451 −26.673854 SiO2 1.560326 89.0 29 233.589947−0.999701 91.7 30 −199.473771 −82.749765 SiO2 1.560326 101.9 313119.046646 −0.999910 98.4 32 −163.659814 −97.677532 SiO2 1.560326 94.733 −539.497284 −13.721631 71.9 34 641.496250 −9.999860 SiO2 1.56032670.4 35 −263.409377 −22.259722 65.3 36 545.844495 −9.999869 SiO21.560326 65.6 37 −150.000000 −51.094164 69.1 38 122.880466 −44.260917SiO2 1.560326 72.0 39 175.327963 −1.012444 98.0 40 452.453640 −29.086710SiO2 1.560326 112.9 41 252.725536 −0.999886 117.1 42 −302.044457−64.007583 SiO2 1.560326 139.9 43 305.246700 −6.812911 140.0 44−260.892072 −48.787934 SiO2 1.560326 137.1 45 −63738.396409 −13.368774134.7 46 0.000000 12.334911 129.6 47 −172.500300 −51.001701 SiO21.560326 121.3 48 −373.082563 −16.645823 113.1 49 −112.356012 −65.439167SiO2 1.560326 89.5 50 −320.098458 −1.015712 65.8 51 −54.459312−52.887119 SiO2 1.560326 47.4 52 0.000000 −1.000000 H2O 1.470000 16.4 530.000000 0.000000 15.0 Aspherical Constants Surface 8 15 20 22 23 K 0 00 0 0 C1 6.337290E−08 −2.289285E−08 3.811590E−08 −1.408703E−083.501090E−08 C2 −2.575433E−12 1.432217E−12 −4.102034E−14 −1.345623E−12−1.799694E−12 C3 7.627829E−17 −1.580637E−16 −3.621641E−17 −1.762608E−161.094631E−16 C4 1.450407E−20 −5.394281E−22 2.030758E−21 −3.325862E−20−9.420105E−21 C5 −1.543958E−24 3.014031E−25 −6.452103E−26 −2.817912E−256.875122E−25 C6 4.707930E−29 −1.444085E−29 1.025805E−30 −4.961418E−28−2.101511E−29 Surface 25 26 33 35 37 K 0 0 0 0 0 C1 3.501090E−08−1.408703E−08 −3.145690E−08 −2.578536E−07 1.520597E−07 C2 −1.799694E−12−1.345623E−12 4.063324E−12 −2.457425E−11 1.942927E−11 C3 1.094631E−16−1.762608E−16 −1.462751E−15 2.999712E−15 −4.917419E−15 C4 −9.420105E−21−3.325862E−20 7.092121E−20 −3.983598E−19 8.521190E−19 C5 6.875122E−25−2.817912E−25 7.491721E−24 −1.456563E−23 −8.041405E−23 C6 −2.101511E−29−4.961418E−28 −1.243101E−27 5.238173E−27 3.671590E−27 Surface 40 43 4850 K 0 0 0 0 C1 −1.092116E−08 −3.583758E−08 4.087867E−08 −1.635385E−07C2 −9.361667E−13 3.835468E−14 −5.710459E−12 1.465150E−12 C3−4.749385E−17 −2.007621E−17 3.741501E−16 −2.027656E−15 C4 −4.357573E−221.168203E−21 −1.621453E−20 2.148610E−19 C5 1.246971E−25 −2.521599E−264.063636E−25 −1.061058E−23 C6 −1.486578E−30 1.420584E−31 −4.118469E−30−6.881746E−28 Decentering and tilt Surface Δx Δy Δz alpha beta 21 0 0 045 0 27 0 0 0 45 0

TABLE 6 NA 1.2 Object height 60 Wavelength 193.306 Surface RadiusThickness Material Refractive index Half diameter 0 0.000000 50.00000060.0 1 0.000000 8.000000 SiO2 1.560326 75.8 2 0.000000 50.933772 77.4 3−727.775952 25.801782 SiO2 1.560326 91.7 4 −216.030845 0.999536 94.2 5211.040976 39.710297 SiO2 1.560326 100.0 6 −1076.869902 0.999021 98.8 7112.711195 31.326403 SiO2 1.560326 87.5 8 214.295126 0.999021 82.2 966.802488 35.387213 SiO2 1.560326 65.6 10 66.108395 78.774319 54.5 11−55.465504 9.999279 SiO2 1.560326 46.8 12 −298.251888 8.105868 72.0 13−253.844073 52.611973 SiO2 1.560326 80.0 14 −100.868104 0.999465 90.1 15−254.089180 50.743218 SiO2 1.560326 105.4 16 −122.616553 0.999454 113.017 −325.389469 35.368071 SiO2 1.560326 127.5 18 −192.299059 0.999384130.8 19 857.924664 43.506291 SiO2 1.560326 134.2 20 −402.1829660.999406 133.9 21 176.032352 46.901034 SiO2 1.560326 117.2 22 891.73754971.819796 112.8 23 0.000000 −160.998496 Mirror 69.5 24 −208.477853−20.000004 SiO2 1.560326 53.4 25 −111.736857 −23.422421 54.3 26134.874404 23.422421 Mirror 55.0 27 −111.736857 20.000004 SiO2 1.56032654.3 28 −208.477853 160.998496 53.4 29 0.000000 −65.065512 Mirror 67.830 4804.317970 −34.969769 SiO2 1.560326 101.2 31 223.557361 −0.999140104.7 32 −647.576916 −33.517562 SiO2 1.560326 114.7 33 511.971879−0.999339 115.8 34 −182.695186 −51.687095 SiO2 1.560326 118.0 35−4375.653897 −0.999619 115.4 36 −131.735101 −46.203705 SiO2 1.56032697.8 37 −1809.243103 −4.477930 91.6 38 −573.465666 −9.999876 SiO21.560326 88.1 39 −83.272578 −56.613234 66.8 40 99.102012 −9.999038 SiO21.560326 66.0 41 −124.605516 −52.681306 67.0 42 96.638032 −42.501820SiO2 1.560326 69.1 43 143.757600 −0.999495 94.1 44 −589.601528−42.492551 SiO2 1.560326 123.1 45 416.503743 −0.999625 125.6 46−393.581824 −32.891473 SiO2 1.560326 135.3 47 929.275942 −0.999694 135.248 −239.988808 −45.788842 SiO2 1.560326 138.8 49 −1114.851901 −57.991878136.9 50 0.000000 35.538482 125.2 51 −256.373888 −39.977376 SiO21.560326 125.8 52 −2489.189597 −0.999817 122.9 53 −112.292298 −50.358269SiO2 1.560326 100.7 54 −179.732403 −23.614201 86.6 55 −186.994041−26.151602 SiO2 1.560326 79.8 56 2504.333895 −0.998913 74.1 57−52.818237 −54.338932 SiO2 1.560326 47.2 58 0.000000 −1.000000 H2O1.470000 16.4 59 0.000000 0.000000 Aspherical Constants Surface 8 15 2224 25 K 0 0 0 0 0 C1 8.438429E−08 −1.014379E−07 −9.680776E−104.589290E−07 6.275710E−07 C2 −2.229236E−12 2.468382E−12 4.462665E−13−3.839142E−11 −6.326297E−11 C3 5.317063E−16 −1.792692E−16 2.908499E−183.043656E−15 7.577756E−15 C4 −5.325798E−20 4.554263E−21 −1.022012E−216.631085E−19 7.226551E−20 C5 5.933879E−24 −1.724388E−25 4.498781E−26−2.125048E−22 −2.141074E−22 C6 −2.077845E−28 5.778429E−31 −7.354023E−312.274431E−26 2.995536E−26 Surface 27 28 37 39 40 K 0 0 0 0 0 C16.275710E−07 4.589290E−07 −7.232518E−08 −3.945726E−08 −3.396052E−07 C2−6.326297E−11 −3.839142E−11 −2.217467E−13 −3.426461E−12 −1.972920E−11 C37.577756E−15 3.043656E−15 2.847604E−16 −1.874953E−16 3.767085E−15 C47.226551E−20 6.631085E−19 −4.835319E−20 −1.321859E−19 −5.439776E−19 C5−2.141074E−22 −2.125048E−22 3.646996E−24 1.333399E−23 2.984282E−23 C62.995536E−26 2.274431E−26 −1.391467E−28 −5.465124E−28 −2.440112E−27Surface 44 47 54 56 K 0 0 0 0 C1 −1.325605E−08 −4.372799E−08−7.345028E−08 −7.547169E−08 C2 1.550416E−12 8.360768E−13 −1.135658E−11−6.239064E−12 C3 −6.951071E−17 −3.668297E−18 8.060461E−16 1.564526E−15C4 1.294568E−21 −1.473145E−21 −1.202219E−19 −3.045032E−19 C55.461199E−26 7.932242E−26 7.589632E−24 2.788162E−23 C6 −2.663009E−30−1.459442E−30 −3.785640E−28 −1.205165E−27 Decentering and tilt SurfaceΔx Δy Δz alpha beta 23 0 0 0 45 0 29 0 0 0 45 0

What is claimed is:
 1. A catadioptric projection objective formicrolithography for imaging an object field in an object plane onto animage field in an image plane when the object field is illuminated withradiation, comprising: a first partial objective for imaging the objectfield onto a first real intermediate image, a second partial objectivefor imaging the first intermediate image onto a second real intermediateimage, wherein the second partial objective is a catadioptric objectivehaving exactly one concave mirror and having at least one lens, a thirdpartial objective for imaging the second intermediate image onto theimage field, and a first folding mirror for deflecting the radiationfrom the object plane toward the concave mirror and a second foldingmirror for deflecting the radiation from the concave mirror toward theimage plane, wherein at least one surface of a lens of the secondpartial objective has an antireflection coating having a reflectivity ofless than 0.1% for an operating wavelength of between 150 nm and 250 nmand for an angle-of-incidence range of between 0° and 20°, wherein theantireflection coating comprises at least six layers.
 2. Thecatadioptric projection objective according to claim 1, wherein thematerial having a low refractive index is a dielectric material selectedfrom the group consisting of: magnesium fluoride, aluminum fluoride,sodium fluoride, lithium fluoride, calcium fluoride, barium fluoride,strontium fluoride, cryolite, chiolite, and combinations thereof.
 3. Thecatadioptric projection objective according to claim 1, wherein the atleast one surface has a deviation from the marginal ray concentricity ofless than 20°.
 4. The catadioptric projection objective according toclaim 1, wherein the second partial objective has an absolute value ofan imaging scale of between 0.8 and 1.25.
 5. The catadioptric projectionobjective according to claim 1, wherein the concave mirror is arrangedin the region of a pupil plane.
 6. The catadioptric projection objectiveaccording to claim 1, wherein the second intermediate image is arrangedin the region of the second folding mirror.
 7. A projection exposureapparatus for microlithography comprising an illumination system and thecatadioptric projection objective according to claim
 1. 8. Thecatadioptric projection objective according to claim 1, wherein theprojection objective has an image-side numerical aperture NA of at least1.2 when an immersion fluid is positioned between the third partialobjective and the image plane.
 9. The catadioptric projection objectiveaccording to claim 8, wherein the antireflection coating has areflectivity of less than 0.2% for the operating wavelength and for anangle-of-incidence range of between 0° and 30°.
 10. The catadioptricprojection objective according to claim 9, wherein the antireflectioncoating has a reflectivity of less than 0.1% for the operatingwavelength and for an angle-of-incidence range of between 0° and 30°.11. The catadioptric projection objective according to claim 9, whereinthe antireflection coating has a reflectivity of less than 0.05% for theoperating wavelength and for the angle-of-incidence range of between 0°and 20°.
 12. The catadioptric projection objective according to claim11, wherein the antireflection coating has a reflectivity of less than0.02% for the operating wavelength and for an angle-of-incidence rangeof between 0° and 10°.
 13. The catadioptric projection objectiveaccording to claim 11, wherein the six layers of the antireflectioncoating are composed alternately of material having a high refractiveindex and material having a low refractive index.
 14. The catadioptricprojection objective according to claim 9, wherein the first and thirdpartial objectives share a common straight optical axis and wherein thesecond partial objective has an optical axis different from the commonstraight optical axis.
 15. The catadioptric projection objectiveaccording to claim 9, wherein the antireflection coating is differentfrom any coating on any lens surface in the first partial objective. 16.The catadioptric projection objective according to claim 9, wherein theantireflection coating is different from any coating on any lens surfacein the third partial objective.
 17. The catadioptric projectionobjective according to claim 14, wherein the antireflection coating isdifferent from any coating on any lens surface in the first and thirdpartial objectives.
 18. The catadioptric projection objective accordingto claim 17, wherein all of the lenses of the second partial objectivehave lenses surfaces having antireflection coatings.
 19. A projectionexposure apparatus for microlithography comprising an illuminationsystem and the catadioptric projection objective according to claim 18.20. A catadioptric projection objective for microlithography for imagingan object field in an object plane onto an image field in an image planewhen the object field is illuminated with radiation, comprising: a firstpartial objective for imaging the object field onto a first realintermediate image, a second partial objective for imaging the firstintermediate image onto a second real intermediate image, wherein thesecond partial objective is a catadioptric objective having exactly oneconcave mirror and having at least one lens, a third partial objectivefor imaging the second intermediate image onto the image field, a firstfolding mirror for deflecting the radiation from the object plane towardthe concave mirror and a second folding mirror for deflecting theradiation from the concave mirror toward the image plane, means forreducing stray light that would otherwise produce backgroundillumination in the image plane that reduces contrast of the image fieldwhen the object field is illuminated with the radiation, wherein themeans is configured such that, in a center of an image of a squareobject, an intensity of the image is less than 1.1% in comparison withthe maximum intensity within the image field, wherein the square objectin the object field: has an edge length of between 0.8 mm and 1.2 mm; isarranged entirely within the object field when homogeneouslyilluminated; is not luminous; and is imaged with a pupil filling factorσ of between σ=0.2 and σ=0.3 into the image plane, and wherein the meanscomprises an antireflection coating comprising at least six layers. 21.The catadioptric projection objective according to claim 20, wherein theintensity of the image is less than 0.9% in comparison with the maximumintensity within the image field.
 22. The catadioptric projectionobjective according to claim 20, wherein the intensity of the image isless than 0.5% in comparison with the maximum intensity within the imagefield.
 23. The catadioptric projection objective according to claim 20,wherein the six layers of the antireflection coating are composedalternately of material having a high refractive index and materialhaving a low refractive index.
 24. The catadioptric projection objectiveaccording to claim 20, wherein the projection objective has animage-side numerical aperture NA of at least 1.2 when an immersion fluidis positioned between the third partial objective and the image plane.25. A projection exposure apparatus for microlithography comprising anillumination system and the catadioptric projection objective accordingto claim
 24. 26. A catadioptric projection objective formicrolithography for imaging an object field in an object plane onto animage field in an image plane when the object field is illuminated withradiation, comprising: a first partial objective for imaging the objectfield onto a first real intermediate image, a second partial objectivefor imaging the first intermediate image onto a second real intermediateimage, wherein the second partial objective is a catadioptric objectivehaving exactly one concave mirror and having at least one lens, a thirdpartial objective for imaging the second intermediate image onto theimage field, a first folding mirror for deflecting the radiation fromthe object plane toward the concave mirror and a second folding mirrorfor deflecting the radiation from the concave mirror toward the imageplane, means for reducing stray light that would otherwise producebackground illumination in the image plane that reduces contrast of theimage field when the object field is illuminated with the radiation,wherein the means is configured such that, within the image field, amaximum difference between a stray light intensity for a pupil fillingfactor σ of between σ=0.2 and σ=0.3 and a stray light intensity for apupil filling factor σ of between σ=0.8 and σ=1.0 in the image plane isless than 0.3%, and wherein the means comprises an antireflectioncoating comprising at least six layers.
 27. The catadioptric projectionobjective according to claim 26, wherein the projection objective has animage-side numerical aperture NA of at least 1.2 when an immersion fluidis positioned between the third partial objective and the image plane.28. A projection exposure apparatus for microlithography comprising anillumination system and the catadioptric projection objective accordingto claim
 27. 29. A catadioptric projection objective formicrolithography for imaging an object field in an object plane onto animage field in an image plane when the object field is illuminated withradiation, comprising: a first partial objective for imaging the objectfield onto a first real intermediate image, a second partial objectivefor imaging the first intermediate image onto a second real intermediateimage, wherein the second partial objective is a catadioptric objectivehaving exactly one concave mirror and having at least one lens, a thirdpartial objective for imaging the second intermediate image onto theimage field, and a first folding mirror for deflecting the radiationfrom the object plane toward the concave mirror and a second foldingmirror for deflecting the radiation from the concave mirror toward theimage plane, wherein at least one surface of a lens of the secondpartial objective has an antireflection coating having a reflectivity ofless than 0.2% for an operating wavelength of between 150 nm and 250 nmand for an angle-of-incidence range of between 0° and 30°, and whereinthe projection objective has an image-side numerical aperture NA of atleast 1.2 when an immersion fluid is positioned between the thirdpartial objective and the image plane.
 30. The catadioptric projectionobjective according to claim 29, wherein the antireflection coating hasa reflectivity of less than 0.1% for the operating wavelength and forthe angle-of-incidence range of between 0° and 30°.
 31. The catadioptricprojection objective according to claim 29, wherein the antireflectioncoating is different from any coating on any lens surface in the thirdpartial objective.
 32. A projection exposure apparatus formicrolithography comprising an illumination system and the catadioptricprojection objective according to claim 29.